| 摘要 |
An overcurrent protection apparatus for a load circuit can detect an overcurrent with a high accuracy without being influenced by a deviation ±&Dgr;Ron of the on-resistance of a semiconductor element (T1). Supposing that a ratio (R3/R1) between a resistor R3 and a resistor R1 is an amplification factor m, a determination voltage generated by resistors R4, R5 is V4 and the average value of the on-resistance of a MOSFET (T1) is Ron, the overcurrent protection apparatus for a load circuit controls either a current I3 flowing through the resistor R3 or a current IR5 flowing through the resister R5 so that the output signal of a compactor CMP1 is inverted when a current having a value of (V4/m/Ron) flows into the MOSFET (T1). For example, when the deviation ±&Dgr;Ron of the on-resistance has a positive value, either the current I3 is generated by subtracting a current proportional to the deviation ±&Dgr;Ron from a current I1 flowing through the R1 or the current IR5 is generated by adding a current proportional to the deviation ±&Dgr;Ron to a current IR4 flowing through R4. In contrast, when the deviation ±&Dgr;Ron of the on-resistance has a negative value, either the current I3 is generated by adding the current &Dgr;I1 proportional to the deviation ±&Dgr;Ron to the current I1 or the current IR5 is generated by subtracting the current proportional to the deviation ±&Dgr;Ron from the current IR4. |
